Browsing by Subject "wireless"
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Item Adaptive protocols for mobile ad hoc networks(Texas A&M University, 2005-02-17) Holland, Gavin DouglasRecent advances in low-power technologies have resulted in the proliferation of inexpensive handheld mobile computing devices. Soon, just like the Internet empow- ered a whole new world of applications for personal computers, the development and deployment of robust ubiquitous wireless networks will enable many new and exciting futuristic applications. Certain to be an important part of this future is a class of networks known as "mobile ad hoc networks." Mobile ad hoc networks (or simply "ad hoc networks") are local-area networks formed "on the spot" between collocated wireless devices. These devices self-organize by sharing information with their neigh- bors to establish communication pathways whenever and wherever they are. For ad hoc networks to succeed, however, new protocols must be developed that are capable of adapting to their dynamic nature. In this dissertation, we present a number of adaptive protocols that are designed for this purpose. We investigate new link layer mechanisms that dynamically monitor and adapt to changes in link quality, including a protocol that uses common control messages to form a tight feedback control loop for adaptation of the link data rate to best match the channel conditions perceived by the receiver. We also investigate routing protocols that adapt route selection according to network characteristics. In particular, we present two on-demand routing protocols that are designed to take advantage of the presence of multirate links. We then investigate the performance of TCP, showing how communication outages caused by link failures and routing delays can be very detrimental to its performance. In response, we present a solution to this problem that uses explicit feedback messages from the link layer about link failures to adapt TCP's behavior. Finally, we show how link failures in heterogeneous networks containing links with widely varying bandwidth and delay can cause repeated "modal" changes in capacity that TCP is slow to detect. We then present a modifed version of TCP that is capable of more rapidly detecting and adapting to these changes.Item An experimental comparison of wireless position locating algorithms based on received signal strength(2009-05-15) Gutierrez, FelixThis thesis presents and discusses research associated with locating wireless devices. Several algorithms have been developed to determine the physical location of the wireless device and a subset of these algorithms only rely on received signal strength (RSS). Two of the most promising RSS-based algorithms are the LC and dwMDS algorithms; however each algorithm has only been tested via computer simulations with different environmental parameters. To determine which algorithm performs better (i.e., produces estimates that are closer to the true location of the wireless device), a fair comparison needs to be made using the same set of data. The goal of this research is to compare the performance of these two algorithms using not only the same set of data, but data that is collected from the field. An extensive measurement campaign at different environments provided a vast amount of data as input to these algorithms. Both of these algorithms are evaluated in a onedimensional (straight line) and two-dimensional (grid) setting. In total, six environments were used to test these algorithms; three environments for each setting. The results show that on average, the LC algorithm outperforms dwMDS in most of the environments. Since the same data was inputted for each algorithm, a fair comparison can be made and doesn?t give any unfair advantage to any particular algorithm. In addition, since the data was taken directly from the field as opposed to computer simulations, this provides a better degree of confidence for a successful realworld implementation.Item Design and implementation of a sub-threshold wireless BFSK transmitter(2009-05-15) Paul, SuganthPower Consumption in VLSI (Very Large Scale Integrated) circuits is currently a major issue in the semiconductor industry. Power is a first order design constraint in many applications. Several of these applications need extreme low power but do not need high speed. Sub-threshold circuit design can be used in these cases, but at such a low supply voltage these circuits exhibit an exponential sensitivity to process, voltage and temperature (PVT) variations. In this thesis we implement and test a robust sub-threshold design flow which uses circuit level PVT compensation to stabilize circuit performance. This is done by dynamic modulation of the delay of a representative signal in the circuit and then phase locking it with an external reference signal. We design and fabricate a sub-threshold wireless BFSK transmitter chip. The transmitter is specified to transmit baseband signals up to a data rate of 32kbps over a distance of 1000m. In addition to the sub-threshold implementation, we implement the BFSK transmitter using a standard cell methodology on the same die operating at super-threshold voltages on a different voltage domain. Experiments using the fabricated die show that the sub-threshold circuit consumes 19.4x lower power than the traditional standard cell based implementation.Item Empirical measurements on a wireless sensor network(2010-12) Tilleman, Matthew John; Aziz, Adnan; McDermott, MarkMy project was to develop a hardware and software platform consisting of client nodes and a base station interconnected wirelessly. The nodes collect physical data for their local environment - I implemented a temperature measurement and a battery level reading. These measurements were placed in a packet which was then relayed via other nodes to the base station. The base station is attached to a USB dongle to a computer which collects the data and stores it into a log file for later analysis. In designing such a network, my goal was to learn about routing protocols, take key concepts learned in classes, such as different modulation schemes and the study of wireless degradation in various environments due to reflections and interference, and explore an implementation of a commercial wireless system. Such a system could be modified to fit a multitude of applications such as environmental data collection for farmers, low power networks for data communication for disaster recovery teams, or sensor networks or implemented in a house to collect data over long period and analyze variances in different regions and implement automated control through a feedback loop. To implement my code, I used TI’s EZ430-RF2500. This development kit contains the TI MSP430F2274, a 16MHz, 16 bit RISC processor which in active mode only pulls 270µA. The MSP430F2274 is coupled with a TI CC2500 which is a 2.4GHz RF transceiver used to communicate with the other devices. The EZ430-RF2500 connects to the computer via a USB dongle with proprietary firmware loaded which allows for programming and serial communication with the computer. I built a network using three devices; one connected to a laptop acting as the access point and two remote devices powered by two AAA batteries acting as the end devices or clients. I performed a study of packet success rates in different environments, specifically inside a residential home, outside in a residential neighborhood and in a rural area. In close ranges (distances less than 50’) there were no noticeable differences in performance between the three environments. I could not exceed 50’ inside the residential environment due to the size of the tested house. Beyond 50’ in the two outside environments, the results surprisingly did not differ greatly; successful transmissions were accomplished at distances only 10’ further in Town Lake; that is that successful transmissions were capable up to 95’ at Town Lake and 85’ in my uban neighborhood. As a representative finding, in the urban environment, the clients were successfully transmitting at an 80% success rate at 80’ pulling 84.48mW (26.4mA at 3.2V) while transmitting with 2-FSK.Item Modeling and design of compact microwave components and systems for wireless communications and power transmission(Texas A&M University, 2004-09-30) Zepeda, PaolaThe contribution of the work here presented involves three main topics: Wireless Power Transmission (WPT) technology, phased array systems, and microwave components design and modeling. The first topic presents the conceptual design of a WPT system at 2.45GHz with 90% efficiency and 1MW of DC output power. Second, a comparative study between 2.45 and 35GHz WPT operation is provided. Finally, the optimization of a taper distribution with reduced thermal constraints on a sandwich transmitter is realized. For a 250- and 375-m antenna radius, 89.7% of collection efficiency with 29% reduction in maximum power density (compared to the Gaussian), and 93% collection efficiency with 39% reduction of maximum power density, are obtained respectively with two split tapers. The reduction in maximum power density and the use of split taper are important to alleviate the thermal problems in high power transmission. For the phased array project, the conceptual design of a small-scale system and in-depth analysis using two main approaches (statistical and field analysis) is realized. Practical aspects are addressed to determine the phased array main design features. The statistical method provides less accurate results than the field analysis since it is intended for large arrays. Careful theoretical analysis led to good correlation between statistical, field analysis and experimental results. In the components chapter, efficient loop transitions used in a patch antenna array are designed at K- and W-band. Measured insertion loss (IL) K-band loop is under 0.4dB. The K- and W-band antenna array measured broadside gains are 23.6dB at 24.125GHz and 25dB at 76.5GHz with return loss under 9.54dB from 24 to 24.4GHz and 12 dB from 75.1 to 77.3GHz, respectively. Also, a multilayer folded line filter is designed at 5.8GHz and compared to planar ring filters. Improved measured bandwidth from 2GHz to 7.5GHz and IL of 1.2dB are obtained with approximately half the size of a planar ring resonator. Thirdly, a simplified switch model is implemented for use in broadband phased-shifters. The model presents very good fit to the measured results with an overall total error under 3%, magnitude error less than 8%, and phase errors less than ?0.4?.Item Wireless, automated monitoring for potential landslide hazards(Texas A&M University, 2007-09-17) Garich, Evan AndrewThis thesis describes research efforts toward the development of a wireless sensor node, which can be employed in durable and expandable wireless sensor networks for remote monitoring of soil conditions in areas conducive to slope stability failures. Commercially available soil moisture probes and soil tilt sensors were combined with low-power, wireless data transmitters to form a self-configuring network of soil monitoring sensors. The remote locations of many slope stability hazard sites eliminates the possibility of real-time, remote monitoring instrumentation that relies on AC power or land-based communication methods for operation and data transfer. Therefore, various power supply solutions and data transfer methods were explored during this research and are described herein. Additionally, sensor modification and calibrations are discussed. Preliminary evaluations of field durability of the pilot instrumentation were undertaken during this research. Geotechnical engineering instrumentation must be able to withstand extreme weather related conditions. The wireless, solar-powered soil moisture and tilt sensor node was installed on the Texas A&M University campus, allowing evaluation of system reliability and instrument durability. Lastly, potential future research and conclusions arising from this research are presented. This research has shown that commercially available wireless instrumentation can be modified for use in geotechnical applications. The development of an active power management system allows for sensors to be placed in remote locations and operated indefinitely, thus creating another option for monitoring applications in geotechnical and environmental problems.